This invention relates to positron emission tomography (xe2x80x9cPETxe2x80x9d) systems, and in particular, to data acquisition in a PET system.
In positron emission tomography (xe2x80x9cPETxe2x80x9d), a radioactive material is placed in the patient. In the process of radioactive decay, this material emits positrons. These positrons travel through the patient until they encounter electrons. When a positron and an electron meet, they annihilate each other. This results in emission of two gamma ray photons traveling in opposite directions. By detecting these gamma ray photons, one can infer the distribution of the radioactive material within the patient.
To detect the photons, the patient is placed along an axis of a ring of detector modules. Each detector module includes detectors that generates an electrical signal when illuminated by a gamma ray photon. This signal is referred to as an event. A processor associated with each module creates an event data packet by compressing information about the event. This event data packet, together with many other event data packets from other modules, is funneled toward a central coincidence processor.
The coincidence processor, which receives event data packets from all detectors on the ring, processes that data. On the basis of the location of the detectors that detected a pair of events and the times of those events, the coincidence processor determines whether that pair of events resulted from an annihilation of a positron and electron within the patient. The coincidence processor then saves the compressed information about each event for later use by an image reconstruction process.
In one aspect according to the invention, a PET scanner includes first and second detector modules for detecting respective first and second events. Each detector module is in communication with corresponding first and second module processors. The first module processor is configured to receive, from the second module processor, a signal indicating the occurrence of the second event, and to provide, to a third module processor, a signal indicating occurrence of the first event.
Embodiments of this aspect of the invention may include one or more of the following features.
The first module processor is configured to determine whether the first and second events define a coincidence. The first module processor is configured to determine whether the detected first event and the received signal, which indicates the second event, define a coincidence.
The first module processor is configured to transmit a request signal to the second module processor when the first module processor considers the first and second events to define a coincidence. In this case, the second module processor is configured to respond to the request signal by transmitting, to the first module processor, additional information about the second event.
The second module processor is configured to send to the first module processor, following detection of the second event, additional information about the second event.
The configuration of module processors can be based on the geometric relationships between detector modules associated with those module processors. For example, in one embodiment, the second and third module processors are selected such that the first detector module and a detector module corresponding to one of the second and third module processors define a field of view that includes a volume into which a patient is to be placed. Or, the first module processor and one of the second and third module processors can be selected such that the first module processor and a detector module corresponding to one of the second and third module processors are opposed to each other on a ring of detector modules.
More than one module processor is designated as a third module processor. The first module processor is configured to provide, to each of a plurality of third module processors, a signal indicating the occurrence of the first event.
More than one module processor is designated as a second module processor. The first module processor is configured to receive, from any one of a plurality of the second module processors, a signal indicating occurrence of the second event at a second detector module associated with that second module processor.
According to another aspect of the the invention, a PET scanner includes a first module processor for detecting a first event occurring at a first detector module and a plurality of remaining module processors, each of which is configured for detecting a second event occurring at a corresponding remaining detector module. The plurality of remaining module processors is divided into first and second subsets. The module processors in the first subset are configured to receive, from the first module processor, a first signal indicating an occurrence of the first event. The module processors in the second subset are configured to provide, to the first module processor, a second signal indicating an occurrence of the second event.
Embodiments of this aspect of the invention may include on or more of the following features.
A coincidence process executes on the first module processor. The coincidence process determines whether the first and second events define a coincidence.
The first module processor is configured to transmit a request signal to a remaining module processor from the second subset. The second subset of remaining module processors includes a selected remaining module processor configured to respond to the request signal by providing additional information about the second event.
The second subset of remaining module processors includes a selected remaining module processor configured to provide additional information about the second event in the absence of a request signal from the first module processor.
The designation of module processors into first and second subsets can depend on the geometric relationship between detector modules associated with those module processors. For example, at least one of the first and second subsets can include a remaining module processor for detecting an event at a detector module that, together with the first detector module, defines a field of view that includes a volume to be occupied by a portion of a patient. Or, at least one of the first subset of remaining module processors can include a remaining module processor for detecting an event at a detector module that is opposed to the first detector module.
According to another aspect of the invention, a method for detecting a coincidence includes collecting, at a first detector module, first information about a first event occurring at the first detector module; collecting, at each of a plurality of remaining module processors second information about a second event occurring at a corresponding remaining detector module; providing, to each remaining module processor from a first subset of the remaining module processors, a first signal indicating an occurrence of the first event, and receiving, from each remaining module processor from a second subset of the remaining module processors, a second signal indicating an occurrence of the second event.
In a PET scanner according to the invention, each module processor acts as both a master and a slave. As a master, each module processor considers events detected at only a few of the available detector modules. This distributed architecture means that each module processor will, when searching for event pairs that form a coincidence, process only a fraction of the total number of events detected at all module processors. Nevertheless, the module processors collectively consider events detected at all the detector modules.
In addition, the procedure for identifying such event pairs does not need to consider the location of the module detector at which an event occurred. Because the master processor only receives event information from selected slave processors, events presented to the master processor for consideration can be pre-qualified by properly selecting the slave processors.
The distributed architecture of the invention also reduces the likelihood that data traffic will be in excess of what the available data links can carry. Because each master is in communication with only a limited number of slaves, there is no need to funnel all data into a single centralized processor. This limits competition for a data link of limited bandwidth.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
Other features and advantages of the invention will be apparent from the following detailed description, and from the claims.